Lithium-ion battery, and electric device using same

Abstract

A lithium-ion battery, and an electric device using the same. The lithium-ion battery comprises a positive electrode, a negative electrode and an electrolyte, wherein an active material of the positive electrode comprises lithium iron manganese phosphate, and the electrolyte comprises a thiophene additive. The chemical structure of the thiophene additive satisfies formula I, wherein at least one group of R1-R4 comprises at least one of an amino, a thienyl, a pyridyl, an acetyl, an amido and an ester group; and the content of the thiophene additive is 0.08-2.80wt% on the basis of the total mass of the electrolyte.

Description

A lithium-ion battery and an electrical device using the same.

[0001] This application claims priority to Chinese Patent Application No. 2024108072961, filed on June 20, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion battery technology, specifically to a lithium-ion battery and an electrical device using the same. Background Technology

[0003] Compared to lead-acid, nickel-cadmium, and nickel-metal hydride batteries, lithium-ion batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in telecommunications, power tools, electric bicycles, electric motorcycles, electric vehicles, special equipment, and special aerospace fields due to their high energy density, high operating voltage, long lifespan, and environmental friendliness. With the widespread use of electronic products, the industry has placed higher demands on the cycle performance of lithium-ion batteries.

[0004] Currently, lithium iron phosphate (LFP) is a promising lithium-ion rechargeable battery. Furthermore, LFP boasts advantages such as high energy density, abundant raw material resources, low cost, environmental friendliness, and high safety. Technical issues

[0005] At higher temperatures or voltages, lithium manganese iron phosphate (LFP) cells experience the John-Teller effect during cell cycling, causing trivalent manganese to be distorted into divalent manganese. This increases the solubility of manganese ions in the electrolyte, making them more likely to migrate to the negative electrode side and be reduced and deposited on the negative electrode surface. This damages the SEI film, accelerates side reactions, and leads to the consumption of a large amount of active lithium, affecting the battery's cycle capacity. Furthermore, the dissolution of manganese ions in LFP can damage the positive electrode structure, resulting in high interfacial impedance and battery capacity decay, thus affecting the battery's cycle stability. Technical solutions

[0006] In a first aspect, this application provides a lithium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte. The active material of the positive electrode includes lithium manganese iron phosphate, and the electrolyte includes thiophene-based additives. The chemical structure of the thiophene-based additives is described below.

[0007] At least one group in R1 to R4 includes at least one of amino, thiophene, pyridinyl, acetyl, amide, and ester groups, and the content of thiophene additives is 0.08 to 2.80 wt% based on the total mass of the electrolyte.

[0008] Secondly, this application provides an electrical device including the aforementioned lithium-ion battery. Beneficial effects

[0009] This application improves the cycle stability of both the positive and negative electrodes by introducing thiophene-based additives that meet the above requirements into the electrolyte. The thiophene-based additives include both a thiophene ring structure and specific groups containing nitrogen, sulfur, and / or oxygen elements with lone pairs of electrons, with these specific groups directly connected to the thiophene ring. Therefore, by using the elements containing lone pairs of electrons in the thiophene-based additives to complex with manganese ions dissolved from the positive electrode material, the content of manganese ions in the electrolyte can be effectively reduced, thereby reducing side reactions between manganese ions and the electrolyte. It also prevents manganese ions from migrating to the negative electrode surface, reducing damage to the SEI film of the negative electrode, inhibiting the reduction of manganese ions to manganese metal at the negative electrode, reducing the amount of manganese metal deposited at the negative electrode, inhibiting the dissolution of manganese ions, enhancing the diffusion of lithium ions in the positive electrode, reducing battery polarization, and reducing the amount of free manganese ions in the electrolyte, thus preventing the deposition of large amounts of manganese metal at the negative electrode. This achieves the goal of simultaneously improving the stability of both the positive and negative electrodes during battery cycling and improving the cycle capacity retention rate of the lithium-ion battery.

[0010] On the other hand, thiophene additives within the aforementioned content range can promote the formation of the SEI film on the negative electrode surface and improve the structural stability of the SEI film, thereby reducing interfacial impedance, improving battery cycle performance, delaying negative electrode aging, and extending the cycle life of batteries using this electrolyte. In particular, after high-temperature storage, manganese in the positive electrode material is more prone to disproportionation, dissolving into the electrolyte in the form of manganese ions. Furthermore, the electrolyte provided in this application also exhibits good heat resistance; even at high temperatures, thiophene additives can still form stable complexes with manganese ions, and the SEI film formed by the thiophene additives still possesses good mechanical properties, improving the battery's high-temperature cycle and high-temperature storage performance, and enhancing capacity retention. Embodiments of the present invention

[0011] In some embodiments, the content of thiophene additives is 0.08wt%, 0.10wt%, 0.25wt%, 0.5wt%, 0.75wt%, 1.0wt%, 1.25wt%, 1.5wt%, 1.75wt%, 2.0wt%, 2.50wt%, 2.80wt%, etc.

[0012] In some embodiments, the number of elements containing lone pairs of electrons in the thiophene additive is not less than two.

[0013] In some embodiments, R1 to R4 may be independently selected from at least one of hydrogen atom, methyl, ethyl, cyclopentyl, cyclohexyl, phenyl, amino, thiophene, pyridyl, acetyl, carboxamide, and ester; and / or, R1 and R2, R2 and R3, or R3 and R4 are each independently cyclic, the ring is a 4- to 6-membered ring, the 4- to 6-membered ring includes cyclic hydrocarbons and / or heterocycles, the heterocycle is a heterocycle containing O, S, or N, and the cyclic hydrocarbon is at least one of cycloalkanes, cyclic alkenes, and benzene.

[0014] In some embodiments, the chemical structure of the thiophene additive includes at least one of cyclopentanothiophene, tetrahydrobenzothiophene, and benzothiophene.

[0015] In some embodiments, the number of elements containing lone pairs of electrons in the thiophene additive is no more than four. The aforementioned thiophene additive exhibits higher reactivity with manganese ions, and the resulting complex has higher chemical stability, effectively reducing the amount of free manganese ions in the electrolyte.

[0016] In some embodiments, the number of elements containing lone pairs of electrons in the thiophene additive is four.

[0017] In some embodiments, the molar ratio of nitrogen to sulfur to oxygen in the thiophene additive is calculated to be 2:1:1. Long-term experiments and verifications have shown that when the molar ratio of nitrogen, sulfur, and oxygen in the thiophene additive meets this ratio, the coordination bond energy in the complex formed by the thiophene additive and manganese ions is larger, resulting in higher stability of the complex. This helps reduce the manganese deposition content on the negative electrode, preventing manganese ions from damaging the SEI film of the negative electrode, thereby reducing the consumption of active lithium and improving the cycle stability of batteries using this electrolyte. In particular, using the above-mentioned thiophene additive in combination with ester additives can also effectively suppress the volume expansion of the negative electrode active material and effectively slow down battery aging.

[0018] In some embodiments, the thiophene additives include 2-amino-5,6-dihydro-cyclopentanopyrothiophene-3-carbonylamide.

[0019] In some embodiments, the mass ratio of thiophene additives to ester additives in the electrolyte is 0.08~2.80:1.0~3.5. During battery charging and discharging, the negative electrode active material is prone to volume changes. Conventional negative electrode SEI films rupture due to these volume changes, leading to a decrease in battery capacity. When the mass ratio of thiophene additives to ester additives falls within the above range, it promotes the formation of anion-rich inorganic film and a dense and stable organic polymeric SEI film on the negative electrode surface. This SEI film possesses excellent flexibility, mechanical properties, and low interfacial impedance, enabling it to adapt to volume changes in the negative electrode active material, effectively isolating the negative electrode from direct contact with the electrolyte, reducing electrolyte and lithium ion consumption and side reactions, and effectively improving battery capacity.

[0020] In some embodiments, the electrolyte further includes ester additives, including at least one selected from vinylene carbonate (VC), vinyl sulfite (ES), vinyl sulfate (DTD), 1,3-propanesulfonyl lactone (1,3-PS), and propenesulfonyl lactone (PST). By introducing ester additives into the electrolyte, this application, in combination with the aforementioned thiophene additives, can enhance the flexibility and mechanical strength of the SEI film formed during battery cycling, thereby reducing the likelihood of SEI film damage and cracking. Furthermore, it can effectively suppress the volume expansion rate of the negative electrode material, effectively improving the battery's cycle performance.

[0021] In some embodiments, the mass ratio of thiophene additives to ester additives in the electrolyte is 0.08~2.80:1.0~3.5. For example, the mass ratios of thiophene additives to ester additives are 0.08:3.5, 0.20:3.0, 0.5:2.5, 1.0:2.0, 1.5:1.5, 2.0:1.25, and 2.8:1.0. By adjusting the mass ratio of thiophene additives to ester additives in the electrolyte, the structural stability of the SEI film formed by the battery can be improved, SEI film damage can be reduced, and electrolyte loss due to contact between the electrolyte and the electrodes can be reduced.

[0022] In some embodiments, the content of thiophene additives is 0.10~1.80 wt% based on the total mass of the electrolyte. When the amount of thiophene additives added to the electrolyte is within the above range, the resulting lithium-ion battery has excellent high-temperature storage and cycle performance, and can still maintain excellent usable battery capacity after high-temperature storage and after 1200 charge-discharge cycles.

[0023] In some embodiments, the content of ester additives is 1.00 to 3.50 wt% based on the total mass of the electrolyte. For example, the content of ester additives is 1.00 wt%, 1.50 wt%, 2.00 wt%, 2.50 wt%, 3.00 wt%, and 3.50 wt%. Introducing ester additives within the above-mentioned content range into the electrolyte can improve the film-forming properties of the electrolyte, reduce interfacial impedance, and improve battery cycle performance.

[0024] In some embodiments, the ester additive includes at least one of vinyl sulfate and vinylene carbonate. When this ester additive is used in combination with the above-mentioned thiophene additive, it can promote the formation of a dense, flexible, and low-resistance SEI film on the electrode surface, forming a tight structural layer without increasing battery impedance, inhibiting the co-intercalation and reductive decomposition of the electrolyte on the electrode, and improving the cycle performance of the lithium-ion battery.

[0025] In some embodiments, the ester additive includes vinylene carbonate, and the content of vinylene carbonate is 2.50 wt% based on the total mass of the electrolyte.

[0026] In some embodiments, the electrolyte also includes a lithium salt, the content of which is 10.50 to 13.00 wt% based on the total mass of the electrolyte. For example, the lithium salt content is 10.50 wt%, 11.00 wt%, 11.50 wt%, 12.00 wt%, 12.50 wt%, or 13.00 wt%.

[0027] In some embodiments, the lithium salt includes lithium hexafluorophosphate and lithium bis(fluorosulfonyl)imide, with a mass ratio of lithium hexafluorophosphate to lithium bis(fluorosulfonyl)imide of 10.5~12:0.5~2. The combined use of lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI) can improve the conductivity of the electrolyte and enhance lithium-ion transport efficiency, thereby improving battery output characteristics and extending battery life.

[0028] In some embodiments, the electrolyte further includes an organic solvent, which includes at least one selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). These organic solvents exhibit good compatibility with thiophene-based and ester-based additives, reducing side reactions during battery cycling and improving battery cycle capacity retention.

[0029] In some embodiments, the organic solvent includes at least three of ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC).

[0030] In some embodiments, the electrolyte further includes an organic solvent, including ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC).

[0031] In some embodiments, the mass ratio of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate is 2~3:4~4.5:1.5~2. Electrolytes using organic solvents in the above mass ratio can improve the cycle characteristics and capacity retention of batteries using them after high-temperature storage.

[0032] In some embodiments, the active material of the negative electrode includes at least one of natural graphite, artificial graphite, and silicon carbide.

[0033] In some implementations, the active material of the negative electrode includes artificial graphite.

[0034] In some embodiments, the lithium-ion battery further includes a separator placed between the positive and negative electrodes, the separator comprising at least one of polypropylene, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, and polyethylene.

[0035] In some embodiments, the diaphragm comprises polypropylene.

[0036] Example 1

[0037] This embodiment provides a lithium-ion battery, including a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes, and also includes an electrolyte.

[0038] (1) Electrolyte:

[0039] The composition of the electrolyte is shown in Table 1:

[0040] Table 1. Raw material composition used to prepare the electrolyte in Example 1

[0041]

[0042] Note: The ratios appearing in Table 1 are mass ratios, such as "dimethyl carbonate: methyl ethyl carbonate: ethylene carbonate = 3:4.5:2.5", which means that the mass ratio of dimethyl carbonate, methyl ethyl carbonate and ethylene carbonate is 3:4.5:2.5, and they are mixed together as an organic solvent.

[0043] Among them, 2-(2-thiophene)pyridine has the CAS number 3319-99-1, and its structural formula is shown in Formula II: .

[0044] Prepare the raw materials according to the above composition, and prepare the electrolyte according to the following steps: In a glove box filled with argon, first mix the organic solvent evenly, then add lithium salt, ester additives and thiophene additives to the organic solvent, and mix evenly to obtain the electrolyte.

[0045] (2) Positive electrode:

[0046] The positive electrode includes a positive current collector and a positive active coating. The positive active coating includes positive active material lithium iron manganese phosphate (LiFeMnPO4), conductive agent carbon black (SP), conductive agent carbon nanotubes (CNT), and positive binder polyvinylidene fluoride (PVDF). In the positive active coating, the mass ratio of LiFeMnPO4, SP, CNT to PVDF is 96.0:2.0:0.5:1.5, and the solid content of the positive binder is 1.327%.

[0047] Prepare the raw materials according to the above composition, and then prepare the positive electrode according to the following steps:

[0048] S1. Mix the positive electrode active material, conductive agent SP, and solvent N-methylpyrrolidone (NMP) evenly; then add conductive agent CNT and positive electrode binder to the reaction system in sequence to obtain a positive electrode slurry; then add solvent NMP to the positive electrode slurry to adjust the viscosity of the positive electrode slurry so that the viscosity of the positive electrode slurry is 15000±3000 mPa·s and the fineness is ≤10 μm.

[0049] S2. The positive electrode slurry is coated on the surface of the positive electrode current collector, dried to obtain the positive electrode active coating, and then subjected to post-processing operations such as cold pressing and cutting to obtain the positive electrode.

[0050] (3) Negative electrode:

[0051] The negative electrode includes a negative electrode current collector and a negative electrode active coating. The negative electrode active coating includes graphite as the negative electrode active material, carbon black (SP) as the conductive agent, carboxymethyl cellulose (CMC) as the negative electrode binder, and styrene-butadiene rubber (SBR) as the aqueous dispersant. In the negative electrode active coating, the mass ratio of graphite, SP, CMC and SBR is 96.5:1.5:1.2:0.8, and the solid content of the negative electrode binder is 8.0%.

[0052] Prepare the raw materials according to the above composition, and then prepare the negative electrode according to the following steps:

[0053] S1. Mix the negative electrode active material, conductive agent SP, and solvent N-methylpyrrolidone (NMP) evenly; then add the negative electrode binder to the reaction system in portions, then add deionized water to the reaction system to adjust the viscosity of the reaction system, and finally add the aqueous dispersant SBR to obtain the negative electrode slurry with a viscosity of 4000±1500 mPa·s and a fineness ≤15 μm.

[0054] S2. The negative electrode slurry is coated on the surface of the negative electrode current collector, and after drying, a negative electrode active coating is obtained. After post-processing operations such as cold pressing and cutting, the positive electrode is obtained.

[0055] (4) Lithium-ion batteries:

[0056] The positive electrode, separator, and negative electrode are stacked in sequence to obtain the battery cell through a stacking process. The battery cell is placed in an outer packaging shell, dried, and electrolyte is injected at an electrolyte injection coefficient of 5.8 g / Ah. After vacuum sealing, settling, formation, and capacity testing, a lithium-ion battery is obtained.

[0057] Example 2

[0058] This embodiment refers to the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this embodiment and Example 1 is that, in the preparation of the electrolyte, an equal mass of dithiophene is used instead of the thiophene additive used in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0059] The CAS number for dithiophene is 492-97-7, and its structural formula is shown in Formula III: .

[0060] Example 3

[0061] This embodiment refers to the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this embodiment and Example 1 is that in the preparation of the electrolyte, an equal mass of 2-acetylthiophene is used instead of the thiophene additive used in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0062] Among them, 2-acetylthiophene has the CAS number 88-15-3, and its structural formula is shown in Formula IV: .

[0063] Example 4

[0064] This embodiment refers to the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this embodiment and Example 1 is that, in the preparation of the electrolyte, an equal mass of 3-methylthiophene-2-carboxamide is used instead of the thiophene additive used in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0065] Among them, 3-methylthiophene-2-carboxamide has the CAS number 76655-99-7, and its structural formula is shown in Formula V: .

[0066] Example 5

[0067] This embodiment refers to the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this embodiment and Example 1 is that in the preparation of the electrolyte, an equal mass of 2-amino-5,6-dihydro-cyclopentanothiophene-3-carbonylamide is used instead of the thiophene additive used in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0068] Among them, the CAS number of 2-amino-5,6-dihydro-cyclopentanothiophene-3-carbonylamide is 77651-38-8, and its structural formula is shown in Formula VI: .

[0069] Example 6

[0070] This embodiment refers to the preparation method provided in Example 1 to prepare a lithium-ion battery. The difference between this embodiment and Example 1 is that, in the preparation of the electrolyte, an equal mass of methyl 5-carbamoylthiophene-2-carboxylate is used instead of the thiophene additive used in Example 1. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 1.

[0071] The CAS number for methyl 5-carbamoylthiophene-2-carboxylic acid is 1206087-41-3, and its structural formula is shown in Formula VII: .

[0072] Example 7

[0073] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that in the process of preparing the electrolyte, the content of thiophene additives and organic solvents in the electrolyte is adjusted so that the mass percentage of thiophene additives in the electrolyte is 0.08%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0074] Example 8

[0075] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that in the process of preparing the electrolyte, the content of thiophene additives and organic solvents in the electrolyte is adjusted so that the mass percentage of thiophene additives in the electrolyte is 1.80%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0076] Example 9

[0077] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that in the process of preparing the electrolyte, the content of thiophene additives and organic solvents in the electrolyte is adjusted so that the mass percentage of thiophene additives in the electrolyte is 2.80%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0078] Example 10

[0079] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that, in the preparation of the electrolyte, lithium hexafluorophosphate of equal mass is used instead of lithium difluorosulfonylimide used in Example 5, and the mass percentage of lithium salt in the electrolyte in this embodiment is the same as that in Example 5. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0080] Example 11

[0081] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that, in the preparation of the electrolyte, an equal mass of 1,3-propanesulfonate lactone (1,3-PS) is used instead of the ester additive used in Example 5. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0082] Example 12

[0083] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that, in the preparation of the electrolyte, an equal mass of organic solvent is used instead of the ester additives used in Example 5. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0084] Example 13

[0085] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that in the preparation of the electrolyte, the content of ester additives and organic solvents is controlled so that the mass ratio of ester additives in the electrolyte is 0.8%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0086] Example 14

[0087] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that in the preparation of the electrolyte, the content of ester additives and organic solvents is controlled so that the mass ratio of ester additives in the electrolyte is 1.0%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0088] Example 15

[0089] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that the content of ester additives and organic solvents is controlled during the preparation of the electrolyte so that the mass ratio of ester additives in the electrolyte is 3.5%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0090] Comparative Example 1

[0091] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that, in the preparation of the electrolyte, an equal mass of organic solvent is used instead of the thiophene additive used in Example 5, which means that the electrolyte prepared in this comparative example does not contain thiophene additives. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0092] Comparative Example 2

[0093] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that, in the preparation of the electrolyte, an equal mass of thiophene is used instead of the thiophene-based additives used in Example 5. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0094] Thiophene has the CAS number 110-02-1, and its structural formula is shown in formula VIII: .

[0095] Comparative Example 3

[0096] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that, in the preparation of the electrolyte, an equal mass of 4,6-dimethyldibenzothiophene is used instead of the thiophene additive used in Example 5. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0097] Among them, 4,6-dimethyldibenzothiophene has the CAS number 1207-12-1, and its structural formula is shown in formula IX: .

[0098] Comparative Example 4

[0099] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that in the process of preparing the electrolyte, the content of thiophene additives and organic solvents in the electrolyte is adjusted so that the mass percentage of thiophene additives in the electrolyte is 3.0%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0100] Comparative Example 5

[0101] This embodiment refers to the preparation method provided in Example 5 to prepare a lithium-ion battery. The difference between this embodiment and Example 5 is that in the preparation of the electrolyte, the content of thiophene additives and organic solvents in the electrolyte is adjusted so that the mass percentage of thiophene additives in the electrolyte is 0.05%. The remaining raw material ratios and preparation methods are strictly consistent with those in Example 5.

[0102] Test case

[0103] Test subjects: Lithium-ion batteries provided in Examples 1-12 and Comparative Examples 1-5.

[0104] Test items and test methods:

[0105] (1) Cyclic performance: The test subject was charged to 4.5V at 1.0C constant current and constant voltage at 25℃, and after standing for 5 minutes, it was discharged to 2.5V at 0.1C. The discharged capacity was recorded as the initial capacity. Then, it was charged to 4.5V at 1.0C constant current and constant voltage, and the initial volume of the battery was recorded. The test subject was charged and discharged at 1C at 45℃, with a voltage range of 2.5~4.5V, for 1200 charge-discharge cycles. The discharge capacity of the 1200th cycle was recorded, the capacity retention rate was calculated, the battery was removed, and the volume of the battery after 1200 cycles was recorded. Among them, the capacity retention rate (%) = (discharge capacity of the 1200th cycle / initial capacity) × 100%, and the volume change rate (%) = (volume after cycle - initial volume) / initial volume × 100%.

[0106] (2) High-temperature storage performance: The test subject was charged to 4.5V at 1.0C constant current and constant voltage at 25℃, and after standing for 5 minutes, it was discharged to 2.5V at 0.1C. The discharged capacity was recorded as the initial capacity. Then, it was charged to 4.5V at 1.0C constant current and constant voltage, and the initial volume of the battery was recorded. The test subject was stored at 60℃±2℃ for 90 days in an open circuit. After that, the battery was taken out and the volume of the battery in the hot state was recorded. After standing at room temperature for 2 hours, the cell was charged and discharged at 1.0C, and the discharge capacity was recorded. The capacity retention rate was then calculated. Among them, the capacity retention rate (%) = discharge capacity after storage / initial capacity × 100%, and the volume change rate (%) = (volume after storage - initial volume) / initial volume × 100%.

[0107] (3) Anode manganese deposition: The test subject was charged to 4.5V at 1.0C constant current and constant voltage at 25℃, left to stand for 5 minutes, and then discharged to 2.5V at 0.1C. The anode plate was then removed, soaked in dimethyl carbonate, dried, and weighed to calculate the weight of the anode active material. The anode manganese content was measured by inductively coupled plasma atomic emission spectrometry and recorded as the initial anode manganese deposition. Then, the cells that had been cycled 1200 times and stored for 90 days in (1) and (2) above were removed and discharged to 2.5V. The anode plate was then removed, soaked in dimethyl carbonate, dried, and weighed to calculate the weight of the anode active material. The anode manganese content was measured by inductively coupled plasma atomic emission spectrometry.

[0108] Test results: The composition of the electrolyte provided by the test subjects is shown in Table 2, and the test results are shown in Table 3.

[0109] Table 2. Composition of electrolytes provided by each test subject

[0110]

[0111]

[0112]

[0113] Note: In Examples 1-9, Examples 11-15, and Comparative Examples 1-5, a mixed lithium salt composed of lithium hexafluorophosphate and lithium difluorosulfonylimide in a mass ratio of 11.25:1.5 was used, while in Example 10, a single lithium salt of lithium hexafluorophosphate was used.

[0114] Table 3. Performance test results for this test case

[0115]

[0116] Results analysis:

[0117] Comparing the test results of Examples 1-15 with those of Comparative Examples 1-5 in Table 2, it can be found that the overall performance of the batteries provided in Examples 1-15 is superior to that of the batteries provided in Comparative Examples 1-5. Among the batteries provided in Examples 1-15, the electrolyte provided in Example 5 can effectively reduce manganese deposition on the negative electrode, and the battery provided has the best cycle characteristics and high-temperature storage performance.

[0118] Comparing the overall performance of Examples 1-6 with Comparative Examples 1-3, it can be observed that as the number of elements containing lone pairs of electrons in the thiophene additives increases, the measured amount of manganese deposition and volume expansion rate of the negative electrode in the battery shows a trend of first decreasing and then increasing, while the cycle capacity retention rate and high-temperature storage performance of the battery show a trend of first increasing and then decreasing. Compared with the batteries of Comparative Examples 1-3, the batteries provided in Examples 1-6 exhibit lower amount of manganese deposition and volume expansion rate in the negative electrode and higher cycle capacity retention rate after 1200 cycles and / or after high-temperature storage. This indicates that when using thiophene additives with at least two lone pairs of electrons, the activity of thiophene additives in complexing with manganese ions can be effectively improved, and the content of manganese ions in the electrolyte can be effectively reduced, thereby reducing the side reactions between manganese ions and the electrolyte and improving the cycle performance of the battery. As can be seen from the performance indicators of Comparative Examples 1-3 in Table 3, the negative electrode manganese deposition amount of Comparative Examples 1-3 is relatively high, and the battery cycle performance is poor. This is because the electrolyte provided does not use thiophene additives or uses thiophene compounds containing only one lone pair electron as thiophene additives. As a result, the cycle performance and high-temperature storage performance of the batteries in Comparative Examples 1-3 are not as good as those of the batteries in Examples 1-6. Among them, compared with the thiophene additive used in Comparative Example 3, the thiophene additive used in Comparative Example 2 has less steric hindrance. Therefore, the complexation activity of the thiophene additive with manganese ions in Comparative Example 2 is higher than that in Comparative Example 3. This is reflected in the fact that the manganese deposition amount of Comparative Example 2 is lower than that of Comparative Example 3 when cycling at 45°C and stored at 60°C.

[0119] Comparing the performance indicators of Examples 5, 7-9, and Comparative Examples 4-5 in Table 3, it can be found that as the content of thiophene additives in the electrolyte increases, the overall performance of the lithium-ion battery shows a trend of first increasing and then decreasing. Compared with the batteries of Comparative Examples 4-5, the batteries of Examples 7-9 have higher capacity retention, better high-temperature storage performance, and lower volume expansion rate. Comparing the performance indicators of the batteries provided in Example 5 and Example 10, it can be found that the overall performance of the battery of Example 5, which uses a mixed lithium salt, is better than that of the battery of Example 10, which uses a single lithium salt. Among them, the electrolyte used in the battery provided in Comparative Example 4 contains more thiophene additives, which increases the battery impedance and ultimately affects the normal cycle performance of the electrolyte, resulting in a lower cycle capacity retention rate of the battery of Comparative Example 4.

[0120] In the batteries of Examples 5 and 12-15, the battery of Example 12 exhibited a higher volume expansion rate, indicating that ester additives and thiophene additives have a synergistic effect in the electrolyte, effectively suppressing the volume expansion of the negative electrode active material and effectively slowing down battery aging. Table 3 shows that the cycling performance indicators of the batteries of Examples 5, 13-15 at 45°C are similar. However, the performance indicators of the batteries of Examples 5 and 14-15 after high-temperature storage are superior to those of Example 13. In particular, the amount of negative electrode manganese deposition in Examples 5 and 14-15 after high-temperature storage is lower than that in Example 13. This indicates that when the mass ratio of thiophene additives to ester additives falls within the range of 0.08-2.80:1.0-3.5, it can improve the structural stability of the SEI film formed in the battery, enhance the cycle characteristics of the battery, and promote the complexation of thiophene compounds with manganese ions.

Claims

1. A lithium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte, wherein the active material of the positive electrode comprises lithium manganese iron phosphate, and the electrolyte comprises a thiophene additive, wherein the chemical structure of the thiophene additive satisfies formula I: At least one of the groups in R1 to R4 includes at least one of amino, thiophene, pyridinyl, acetyl, amide, and ester groups, and the content of the thiophene additive is 0.08 to 2.80 wt% based on the total mass of the electrolyte.

2. The lithium-ion battery of claim 1, wherein, In the chemical structure of the thiophene additive, the following conditions are met: R1~R4may be independently selected from at least one of a hydrogen atom, a methyl group, an ethyl group, a cyclopentane group, a cyclohexane group, a phenyl group, an amino group, a thiophene group, a pyridine group, an acetyl group, a carboxamide group, and an ester group; R1and R2, R2and R3, or R3and R4may independently form a ring, respectively, the ring being a 4~6-membered ring, the 4~6-membered ring including at least one of a cyclic hydrocarbon and / or a heterocycle, the heterocycle being an O-, S-, or N-containing heterocycle, and the cyclic hydrocarbon being a cycloalkane, a cycloalkene, or a benzene.

3. The lithium-ion battery of claim 1, wherein, The number of elements containing a lone pair of electrons in the thiophene additive is not more than 4.

4. The lithium-ion battery of claim 3, wherein, According to a molar ratio, in the thiophene additive, the number of nitrogen elements: the number of sulfur elements: the number of oxygen elements = 2:1:

1.

5. The lithium-ion battery of claim 1, wherein, The electrolyte further includes an ester additive, the ester additive including at least one of vinylene carbonate, vinyl sulfite, vinyl sulfate, 1,3-propane sulfone lactone, and propylene sulfone lactone.

6. The lithium-ion battery of claim 5, wherein, In the electrolyte, the mass ratio of the thiophene additive to the ester additive is 0.08~2.80:1.0~3.

5.

7. The lithium-ion battery of claim 5, wherein, The ester additive includes at least one of vinyl sulfate and vinylene carbonate.

8. The lithium-ion battery of claim 1, wherein, The electrolyte further includes a lithium salt, and the content of the lithium salt is 10.50~13.00wt% based on the total mass of the electrolyte.

9. The lithium-ion battery of claim 8, wherein, The lithium salt includes lithium hexafluorophosphate and lithium bisfluorosulfonimide, and the mass ratio of the lithium hexafluorophosphate to the lithium bisfluorosulfonimide is 10.5~12:0.5~2.

10. A device powered by electricity, including the lithium ion battery according to any one of claims 1~9.

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